Juxtacrine signalling via Notch and ErbB receptors in the switch to fate commitment of bone marrow-derived Schwann cells.

The phenotypic instability of adult tissue-derived Schwann cell-like cells (SCLCs) as revealed upon withdrawal of glia-inducing culture supplements limits their clinical utility for cell therapy and disease modelling. We previously overcame this limitation by co-culturing bone marrow-derived SCLCs with neurons purified from developing rat and subsequently human sensory neurons such that direct contact between cell types accomplished the cell-intrinsic switch to the Schwann cell fate. Here, our search for juxtacrine instructive signals found both Notch ligands and neuregulin-1 type III localized on the surface of DRG neurons via live cell immunocytochemistry. Bypassing ligand-induced release of the Notch intracellular domain (NICD) by transient transfection of SCLCs with the pAdlox/V5-His-NICD construct was shown to upregulate ErbB2/3. Interaction of ErbB2/3 with neuregulin-1 type III (NRG1 type III) as presented on neurons then mediated the switch to the Schwann cell fate as demonstrated by expression of S100β/p75/ Sox10/Krox20. In contrast, treatment of cocultures with γ-secretase inhibitor perturbed Notch signalling in SCLCs and consequently deterred both upregulation of ErbB2/3 and the transition to the Schwann cell fate. Taken together, juxtacrine signalling via Notch is key to the upregulation of ErbB receptors for neuregulin-driven commitment of SCLCs to the Schwann cell fate.